In the packaging industry, for example, it is customary to treat a moving material web in different ways. During the manufacture of sterile packing containers from a material web the material web is usually sterilized before the conversion to individual packing containers. The sterilization is carried out with the help of a chemical sterilizing agent, e.g. hydrogen peroxide, which is supplied to the material web and is removed again after a certain period of treatment with the help of hot air. In the process the web passes into a chamber wherein one or more nozzles (so-called air knives) for hot air are directed towards the web. The chamber is also provided with an outlet for the treatment air and the sterilizing agent removed from the web. It is very important that during the treatment the web does not come into contact either with the nozzle or other parts in the chamber, since this results in damage to the web and possible loss of sterility. Since the amount of air as well as the air velocity have to be relatively high in order to remove the sterilizing agent effectively from the web, vigorous and not easily controllable air flows occur inside the chamber which render it very difficult to provide the web with a steady movement through the chamber, especially in the region where the air knife or the outlet from the chamber are situated. It is ideal if the web can be made to "float" in a calm and steady manner through the chamber without coming into contact at any point with neighbouring mechanical elements. Up to now it has been very difficult to achieve this, and it is generally desirable to provide a treatment chamber which makes this possible.